1. Field of the Invention
The present invention relates to an apparatus and method for detecting a moving object such as a trespasser.
2. Description of the Related Art
In recent security systems, image monitoring apparatus for detecting trespassers and the like using images picked up by TV cameras have become widely popular. Such popularity owes much to inexpensive apparatuses realized by the remarkable progress of semiconductor techniques and the spread of digital image processing techniques.
In an image monitoring apparatus of this type, in order to detect a trespasser, a changing image portion generated when a trespasser moves within the image must be extracted from the video image. As a conventional method of extracting the changing image portion, a subtraction technique is performed using two time-serial images to extract an image of a changed portion (referred to herein as an image changing area). Furthermore, another method has been proposed. In this method, for areas where a trespasser does not pass, an operator of the monitoring apparatus sets a mask area using, for example, a light pen, to exclude these areas, so that a changing area is extracted from only the remainder of the monitored area to detect a trespasser.
However, in the above conventional apparatus, in order to detect a moving object, the extraction of the changing area is performed by using a single image subtraction. In such a case, even if the changing area is extracted within the limits of an extraction area which is designated beforehand, there was no guarantee that the area always indicates movement by a person. There is a risk of extracting a changing area due to noise caused by, for instance, meteorological conditions such as rain or wind. Consequently, there is a problem in the judgement as to whether or not a trespasser is present, by information related only to the size of the rectangular region of the extracted changing area, is largely dependent on the influence of noise. Thus, the discrimination factor was reduced and, at the same time, this resulted in poor reliability of this type of image monitoring apparatus.